Derby County called police after a man was seen "acting suspiciously" at their training ground ahead of their Championship match.

Leeds United manager Marcelo Bielsa has admitted sending someone to spy on Derby County in training - but insisted it was "not illegal".

Derby called police on Thursday morning following reports that a man was "acting suspiciously" on the perimeter of their training ground, ahead of the two teams' clash in the Championship, which Leeds won 2-0.

The man was escorted away by police and Derby manager Frank Lampard stopped training until the incident was over.

Speaking before Friday evening's match between the promotion rivals, Bielsa said: "It's true it was someone from Leeds United. I am responsible for it."

Lampard said what had happened was "bad" and had "disrupted" Derby's build-up to the game.

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WATCH: Marcelo Bielsa admits he was behind #LUFC spy-gate and that he has been using similar tactics for year.

Bielsa said: "It doesn't matter if this is legal or illegal, or right or wrong. For me, it is enough that Frank Lampard and Derby felt it was not the right thing to do, for me to believe that I didn't behave well.

"Yesterday I talked to Frank Lampard and he said I didn't respect the rules of fair play. I have a different point of view on it, but the important thing is what Frank Lampard and Derby think."

Image:Frank Lampard stopped his training session when the man was spotted

Former Argentina manager Bielsa added: "I am the only one responsible for it, because I didn't ask for the permission of Leeds to do it.

"Without trying to find a justification, I have been using this kind of practice since the qualifiers for the World Cup with Argentina.

"It is not illegal, we have been doing it publicly and we talk about it in the press.

"For some people, it's the wrong thing to do and for other people, it's not the wrong thing to do."

But Lampard said: "We had somebody the day before our first game against them, which we lost 4-1.

"Leeds can beat you 4-1 because they are a fantastic team, but they had someone in the bushes that day. The man was asked to leave but it wasn't followed up like it has been this time."

The former Chelsea midfielder added: "On a sportsman's level, it's bad. If we are going to talk about culturally and say I did it somewhere else and it's fine, I don't believe that. It's disrupted our build-up to the game.

"People will say I am making an excuse, but I will speak like this after the game whether we win, lose or draw.

"The training stopped because the police came on the training ground, then it went away.

"We were training on team tactics, team shape, personnel, how we are going to press, how we will work off the ball, the fact Harry Wilson wasn't training would become evident, so the person who is watching will see all of that.

"I don't think we need to [make a complaint] because he's admitted it. It's up to the league to see how they deal with it."

Image:Elland Road - where the teams played each other on Friday evening

Earlier, Derby said they were "in discussion" with officials from Leeds about what happened.

Derbyshire Police said the man was found "at the perimeter fence of Moor Farm and was spoken to".

The force added : "No arrests were made and the man was sent on his way."

In another tweet, it added, tongue in cheek: "Keeping the team safe to bring home a win against LUFC on 11th!

"Spying is cheating."

An FA spokesperson said: "We are aware of the incident at Derby County's training ground and we will be investigating the matter."